A cooperative study is underway at several USPHS Hospitals involving long-term follow-up of patients with diastolic blood pressure between 90 and 115 mm. Hg. The Seattle USPHS Hospital has screened approximately 400 patients to date and has placed 68 on coded drugs. The protocol provides for half of the group to receive placebo and the other half a combination of rauwolfia-thiazide in order to be able to compare the rate of development of morbid events in the two groups. Each patient agrees to participate in the study only after careful explanation is given of what is involved. In all instances, the patient's interest is protected such that in case of any untoward event, he is immediately withdrawn from the study. All patients are followed much more closely than is customary, with exhaustive examinations and tests being performed at frequent intervals.